Device for protecting an electronic printed circuit board

ABSTRACT

A device is provided for protecting an electronic printed circuit board, which includes at least two layers. The device includes on a layer, at least one conductive part uniformly spread on an insulator layer, the entirety comprising the conductive part and the insulator layer forming a capacitive support presenting a uniform electrical field. The capacitive support is placed roughly on the whole surface of one of the layers of the multi-layered electronic printed circuit board. The capacitive support is configured to deliver a reference capacitance. A capacitive measurement microprocessor detects a variation in capacitance. A transmitter is configured for transmitting a piece of information representing the variation in capacitance when an absolute value of a difference between the measured capacitance and the reference capacitance exceeds a predetermined threshold.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

THE NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

None.

FIELD OF THE DISCLOSURE

The present disclosure pertains to the protection of memory card readingdevices. Memory card reading devices are used in many apparatuses suchas payment terminals, authentication or identification devices or againcontent-reading devices.

The present disclosure pertains more particularly to the securing of themulti-layered electronic printed circuit boards of such memory cardreading devices in order to protect them against any intrusion bymalicious third parties.

BACKGROUND OF THE DISCLOSURE

Apparatuses incorporating memory card reading devices such as paymentterminals include many securing devices and implement methods forensuring that the apparatuses are employed in compliance with the usefor which they are planned and that they comply with security standardslaid down by certification organizations.

For example, in the field of payment terminals for payment cards, themanufacturers have developed solutions for protecting the multi-layeredelectronic printed circuit board or boards (PCBs) of the paymentterminals.

More specifically, a printed circuit board is a carrier, generally aplate, used to electrically connect a set of electronic components toone another in order to obtain a complex electronic circuit. This plateconsists of an assembly of several fine layers of copper separated by aninsulating material. The layers of copper are etched by a chemicalmethod to obtain a set of tracks terminated by chips. The printedcircuit board is often coated with a layer of colored varnish(prepreg+FR4) which protects the tracks from oxidation and possibleshort circuits. The tracks electrically connect different zones of theprinted circuit. The chips, once perforated, set up an electrical linkeither between the soldered components through the printed circuit boardor between the different layers of copper (this is the so-called “via”technique). In certain cases, the non-perforated chips are used tosolder surface-mounted components.

Unfortunately, deterioration has been observed in multi-layeredelectronic printed circuit boards. This deterioration takes the form ofpiercing, scraping or any other intrusive technique aimed at shorting,cutting, snooping, etc. a printed circuit board.

For example, a deterioration may correspond to the cutting of a track ofthe printed circuit of a payment terminal in order to annihilate thedispatch of information aimed at triggering the “attack” mode of thesecured processor of a payment terminal.

In order to protect the multi-layered electronic printed circuit,protection solutions have been developed.

A first protection consists in introducing a sort of wire mesh withactivation on electrical levels. These are fine adjacent tracks coveringthe entire part to be protected. For example, one track can be connectedto VCC and the other to GND. Any piercing of this wire mesh can resultin the cutting of one or other of the links, which would be detected. Itcould even result in shorting between two tracks, which would also bedetected. Numerous variations of this device can be used. The detectioncan be done on voltage levels or on the compliance of the signalstravelling through these tracks.

A second protection consists in introducing a wire mesh similar to thatof the first solution described here above and comparing the voltagecharacteristics of a signal sent at one end of the mesh with thecharacteristics of a signal received at the other end.

The drawback of these solutions lies in the fact that there is a space,however tiny it may be, between the different tracks. This enables apossible shorting or again piercing without activation on an electricallevel or again without modification of the characteristics of the signalreceived at the end of the wire mesh as compared with thecharacteristics of the signal sent at another end.

Thus, to date, the inventors have not identified any already existingsimple solution for providing efficient protection to a multi-layeredelectronic printed circuit board against any intrusion by maliciousthird parties.

SUMMARY

An exemplary embodiment of the invention does not have these drawbacksof the prior art.

An embodiment of the invention pertains to a device for protecting anelectronic printed circuit board, said electrical printed circuit boardcomprising at least two layers. According to an embodiment of theinvention, such a device comprises:

-   -   at least one conductive part uniformly spread on an insulator        layer, the entirety comprising the conductive part and the        insulator layer forming a capacitive support presenting a        uniform electrical field, said capacitive support being placed        roughly on the whole surface of one of the layers of the        multi-layered electronic printed circuit board, said capacitive        support being configured to deliver a reference capacitance;    -   a capacitive measurement microprocessor electrically connected        to said at least one capacitive support, said at least one        microprocessor being configured to detect a variation in        capacitance of said at least one capacitive support;    -   means for transmitting a piece of information representing said        variation in capacitance when an absolute value of a difference        between said measured capacitance and said reference capacitance        exceeds a predetermined threshold.

According to one particular embodiment, said device for protecting usesan existing support (wire mesh) and performs a measurement ofcapacitance on said support.

Thus, it is not necessary to make modifications to this circuit toimplement protection.

According to one particular characteristic of an embodiment of theinvention, said device for protecting further comprises calibrationmeans delivering said reference capacitance.

Thus, it is possible to subsequently measure a variation relatively tothis reference.

According to one particular characteristic, said device for protectingfurther comprises a system of compensation for ambient conditionsmodifying said reference capacitance as a function of a predeterminedcriterion.

According to one particular embodiment, said at least one capacitivesupport is positioned on an internal layer of said printed circuit.

Thus, an embodiment of the invention offers protection within theprinted circuit itself.

According to one particular characteristic, said at least one capacitivesupport is deployed in a full plane.

According to one particular characteristic, said at least one capacitivesupport is deployed as a lattice.

According to another aspect, an embodiment of the invention alsopertains to a method for protecting an electronic printed circuit board,said printed circuit comprising at least two layers. According to anembodiment of the invention, such a method comprises:

-   -   a step for laying out at least one conductive part uniformly        spread on an insulator layer, the entirety comprising the        conductive part and the insulator layer forming a capacitive        support presenting a uniform electrical field, said capacitive        support being placed roughly on the whole surface of one of the        layers of the multi-layered electronic printed circuit board,        said capacitive support being configured to deliver a reference        capacitance;    -   a step for capacitive measuring implemented by a capacitive        measurement microprocessor electrically connected to said at        least one capacitive measurement support, said at least one        microprocessor being configured to detect a variation in        capacitance of said at least one capacitive support;    -   a step for transmitting a piece of information representing said        variation in capacitance, when an absolute value of a difference        between said measured capacitance and said reference capacitance        exceeds a predetermined threshold.

According to one particular characteristic, said method for protectingfurthermore comprises a calibration step delivering said referencecapacitance.

According to another form, an embodiment of the invention pertains to apayment terminal characterized in that it comprises at least one devicefor protecting as referred to here above.

An embodiment of the invention also pertains to a computer programcomprising program code instructions to implement the method forprotecting as referred to here above, when the program is executed by aprocessor.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages shall appear more clearly from thefollowing description of a preferred embodiment, given by way of asimple illustratory and non-exhaustive example, and from the appendeddrawings, of which:

FIG. 1 illustrates a device for protecting according to an embodiment ofthe invention;

FIG. 2 illustrates calibration curves of the protection device accordingto an embodiment of the invention;

FIGS. 3A and 3B respectively present a capacitive support according toan embodiment of the invention as well as a section of the structure ofa multi-layered electronic printed circuit board;

FIG. 4 illustrates the method for protecting according to an embodimentof the invention;

FIG. 5 is a schematic view of a payment terminal according to anembodiment of the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

1. Reminder of the Principle of an Embodiment of the Invention

An embodiment of the invention proposes to efficiently and simplyprotect the layers of a multi-layered electronic printed circuit boardby using a device for protecting implementing capacitive measurement ofat least one conductive part uniformly spread on an insulator layer, theentirety comprising the conductive part and the insulator layer forminga capacitive support presenting a uniform electrical field, thecapacitive support being placed roughly on the whole surface of one ofthe layers of the multi-layered electronic printed circuit board.

Since the device for protecting implements a capacitive measurement, anintrusion, by shorting or by piercing for example, is detected becausethe intrusion modifies the reference capacitance of the capacitivesupport beyond a predetermined threshold.

According to an embodiment of the invention, the device for protectingan electronic printed circuit board comprises a capacitive support, acapacitive measurement microprocessor and a transmitter configured fortransmitting a piece of information reporting a variation in thecapacitance of the capacitive support beyond a predetermined threshold,in other words reporting an intrusion by a malicious third party.

According to one embodiment of the invention, the capacitive support isdeployed on a layer of the printed circuit in a full plane.

According to another embodiment, a capacitive support in the form of alattice is considered. It is also possible to consider a capacitivesupport in the form of a single copper track.

According to an embodiment of the invention, the protection device iscapable of protecting an electronic printed circuit comprising severalsuperimposed layers of printed circuit connected to one another byburied vias. Such a protection device can take any form whatsoever. Theshape of the device can be adapted to the printed circuit board to beprotected.

Here below, we present an embodiment of a device for protectingaccording to the invention. It is clear however that the invention isnot limited to this particular application, but can also be implementedin many other contexts of protection of electronic printed circuitboards and more generally in any case where the characteristics listedhere below are of interest.

2. Description of an Embodiment of a Device

2.1 Structure of the Device for Protecting

Referring to FIG. 1, we present an embodiment in which the device forprotecting 10 first of all comprises a capacitive support 12corresponding to a full plane and being positioned on a layer 11 of theelectronic printed circuit board of a payment terminal for example.

A capacitive support corresponding to a full plane takes the form of acapacitive surface. More specifically, a surface capacitive technologyconsists for example of a uniform conductive coating on an insulator.During use, electrodes placed on the edge of the insulator distribute alow-voltage current equally throughout the conductive layer, thuscreating a uniform electrical field. When an object comes into contactwith or approaches the surface, this draws the current from every sideof the electrical field.

Optionally, a controller computes the coordinates of the contact bymeasuring the current. It then transmits these coordinates to thesecured processor of the payment terminal.

Besides, calibration means (such as a circuit) 15, electricallyconnected to the capacitive support, enable the reference capacitance ofthis support to be evaluated. The calibration circuit 15 shall bedescribed in greater detail here below.

In addition, the device for protecting according to an embodiment of theinvention also has a capacitive measurement microprocessor 13electrically connected to the capacitive support 12 and to the ground16. Such a measurement microprocessor uses for example a capacitivesensor corresponding to a probe to measure the capacitance of thecapacitive support.

Such a probe may for example be made with a flat measurement electrodesurrounded by a guard ring. The electrode then, with the capacitivesupport, forms a plane capacitor. A guard electrode contained in theguard ring is placed around the measurement electrode, and its potentialis taken to the same value in order to improve the linearity by makingthe field lines normal (i.e. perpendicular) to the measuring electrode.The guard electrode thus eliminates edge effects.

Through these measuring means (including the microprocessor) 13, avariation of the capacitance of the capacitive support is detected. Thisvariation is for example obtained by comparing the measured capacitancewith the reference capacitance determined by the calibration circuit 15.This measurement is preferably done in real time in order toinstantaneously alert the secured processor of a payment terminalthrough transmitter 14.

Independently of the measurement frequency selected by the user, all themeasurements are driven by a computer program recorded within themeasuring means.

More specifically, the measuring microprocessor determines a differencebetween the capacitance of the capacitive support measured by themeasuring microprocessor 13 and the reference capacitance preliminarilydetermined by the calibration circuit. If the absolute value of thisdifference exceeds a predetermined threshold S, the transmitter of thedevice for protecting according to an embodiment of the invention tellthe secured processor of the secured terminal to go into “attack” mode.

Thus, the device for protecting according to an embodiment of theinvention makes it possible to determine any contact with or approachtowards the capacitive support positioned on a layer of the electronicprinted circuit board to be protected. In particular, any intrusion by amalicious third party will be detected, because this intrusion,especially by cutting, shorting or by scraping, significantly modifiesthe capacitance of the capacitive support.

Furthermore, this device for protecting makes use of the capacitivesupport and the capacitive measurement by avoiding implementation of acomplex geometrical routing or by not using hardware that can easilydeteriorate.

2.2 Calibration of the Considered Capacitive Support

The calibration implemented by the calibration circuit 15 is neededbecause the value of the capacitance is sensitive.

Indeed, it is known that the value of the capacitance varies accordingto different factors. For example, the capacitance of a capacitivedetector varies as a function of the charge hysteresis due to themagnetization of a material, the effect of a battery of the paymentterminal or the temperature, humidity, aging especially by oxidation ofthe materials constituting the capacitive detector, etc.

FIG. 2, presenting an example of calibration curves of the device forprotecting according to an embodiment of the invention, represents theprocedure implemented by the calibration circuit delivering thereference capacitance of the capacitive support.

The calibration circuit measures 21 (for example in a manner similar tothat used by the above-described measurement means) the capacitance ofthe capacitive support as a function of time. The measurement curve 21shown in FIG. 2 attests to the fact that the capacitance varies as afunction of time, especially as a function of the ambient temperature.

The calibration circuit takes the average of the capacitance measurementdata on the measurement curve so that a reference value Ref is obtained.

In addition, the calibration circuit determines for example a variationthreshold S of capacitance beyond which the variation in capacitance isabnormal. Thus, the calibration circuit determines the range of value ofcapacitance centered on the reference value making it possible to attestto a “normal” and secured operation of the printed circuit of thepayment terminal.

Preferably, the reference value and the predetermined threshold S arerecorded in a memory and transmitted to the measuring means so thatthese means determine an intrusion by a malicious third party aimed atdamaging the electronic printed circuit board.

Optionally, the calibration circuit further includes a system ofenvironmental compensation aimed at adapting the reference value andpredetermined threshold value S as a function of a parameter selected bythe user of the payment terminal.

For example, since the ambient temperature in Singapore is verydifferent from the temperature in Stockholm, the user adapts thecapacitance reference and the authorized range of capacitance variationto the location.

Similarly, in another example, the user can adapt this range ofvariation as and when the payment terminal ages, according to themanufacturer's recommendations set forth in a user's instruction sheet.

3. Alternative Embodiments

3.1 Type of Capacitive Support

In another embodiment, the capacitive support may take the form of alattice of very fine (less than 10 μm) conductive wires buried betweenlayers of insulator, for example glass or laminated plastic films, asillustrated in FIG. 3A.

Such a lattice 32 may be plane or three-dimensional with a mesh more ofgreater or lesser density.

A capacitive support taking the form of a single copper track (notshown) can also be used.

Furthermore, the device for protecting according to an embodiment of theinvention can also be electrically connected to a printed circuit boardhaving an existing capacitive support constituted by a conductive partand an insulator part. In this case, the protection device of anembodiment of the invention places electrodes on the edge of theinsulator in order to distribute a low-voltage current equallythroughout the conductive part, thus creating a uniform electricalfield. The existing support is thus made capacitive.

3.2 Arrangement of the Capacitive Support

Preferably, the capacitive support is on an internal layer 34 situatedfor example directly beneath an external layer 33 bearing a groundplane.

Indeed, this arrangement is used especially to protect the capacitivesupport and ensure a more stable measurement of the capacitance. Thelower layers 35, i.e. the internal layers situated beneath the layerbearing the capacitive support, are therefore protected againstintrusions by malicious third parties.

According to one alternative embodiment, the capacitive support can alsobe deployed in a “deeper” internal layer, subject to a ground planebeing inserted on a directly neighboring layer so as to protect thecapacitive support from possible electromagnetic disturbance due tointernal electronic circuits (for example tracks) of the multi-layeredelectronic printed circuit board.

Depending on the level of protection sought, the number of capacitivesupports implemented for a printed circuit board can be great. Forexample, each layer of the printed circuit board can carry a capacitivesupport in order to determine the depth of the intrusion.

In this case, the measuring means of each of the capacitive supports maysuccessively perform measurements of capacitance of each layer as afunction of the depth of the layer considered.

4. Description of an Embodiment of the Method for Protecting

Referring to FIG. 4, we present the method for protecting 40 anelectronic printed circuit board according to an embodiment of theinvention.

Such a method comprises:

-   -   a step 41 for placing at least one capacitive support on a layer        of the printed circuit board of the payment terminal,    -   a calibration step 42 delivering the reference capacitance of        the capacitive support,    -   a capacitive measurement step 43 implemented by a capacitive        measurement microprocessor electrically connected to the        capacitive support, the microprocessor being configured to        detect a variation in capacitance of the capacitive support,    -   a step 44 for transmitting a piece of information “attack!”        representing the variation in capacitance when an absolute value        of a difference between the measured capacitance and the        reference capacitance exceeds a predetermined threshold.

In addition, the calibration step could be reiterated according to autilization procedure known by the user.

According to one particular embodiment, the calibration step furthercomprises a step of environmental compensation aimed at taking intoaccount the natural influence of certain parameters such as: the chargehysteresis due to the magnetization of a material, the effect of abattery of the payment terminal, or again temperature, humidity, ageingespecially through the oxidation of the materials constituting thecapacitive support, etc.

Referring to FIG. 5, we present an embodiment of a payment terminal.

Such a terminal comprises a memory 51 constituted by a buffer memory, aprocessing unit 52, equipped for example with a microprocessor anddriven by the computer program 53 implementing the protection method ofan embodiment of the invention.

At initialization, the computer program code instructions 53 are loadedfor example into a RAM and then executed by the processor of theprocessing unit 52. The processing unit 52 inputs at least one piece ofinformation I, such as location zone identifiers. The microprocessor ofthe processing unit 52 implements the steps of the protection methoddescribed here above according to the instructions of the computerprogram 53 to deliver a piece of processed information T such as thedetection of an attack leading to the elimination of the protected data.To this end, in addition to the buffer memory 51, the terminal comprisesat least one capacitive support placed on a layer of said printedcircuit, said at least one capacitive support being configured todeliver a reference capacitance, a capacitive measurement microprocessorelectrically connected to said at least one capacitive support, said atleast one microprocessor being configured to detect a variation incapacitance of said at least one capacitive support, the transmitter fortransmitting a piece of information representing said variation incapacitance when an absolute value of a difference between said measuredcapacitance and said reference capacitance exceeds a predeterminedthreshold.

These elements are driven by the microprocessor of the processing unit52. Although the present disclosure has been described with reference toone or more examples, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the scopeof the disclosure and/or the appended claims.

The invention claimed is:
 1. A device for protecting an electronicprinted circuit board, said electrical printed circuit board comprisingat least two layers, wherein the device comprises: a conductive partuniformly spread on an insulator layer, the entirety comprising theconductive part and the insulator layer forming a capacitive supportpresenting a uniform electrical field over the whole surface of one ofthe layers of the electronic printed circuit board, said capacitivesupport being placed on the whole surface and being configured todeliver a reference capacitance for the whole surface; a capacitivemeasurement microprocessor electrically connected to said capacitivesupport, said microprocessor being configured to detect a variation incapacitance of said capacitive support for said whole surface; and atransmitter configured for transmitting a piece of informationrepresenting said variation of capacitance when an absolute value of adifference between a capacitance measured by said capacitive measurementmicroprocessor and said reference capacitance exceeds a predeterminedthreshold.
 2. The device for protecting according to claim 1, whereinthe device further comprises calibration means delivering said referencecapacitance.
 3. The device for protecting according to claim 1, whereinsaid capacitive support is positioned on an internal layer of saidprinted circuit.
 4. The device for protecting according to claim 1,wherein said capacitive support comprises a uniform conductive coatingforming a full plane over the whole surface.
 5. The device forprotecting according to claim 1, wherein said capacitive support isdeployed as a lattice.
 6. A method for protecting an electronic printedcircuit board, said printed circuit comprising at least two layers,wherein the method comprises: a step of laying out a conductive partuniformly spread on an insulator layer, the entirety comprising theconductive part and the insulator layer forming a capacitive supportpresenting a uniform electrical field over the whole surface of one ofthe layers of the electronic printed circuit board, said capacitivesupport being placed on the whole surface and being configured todeliver a reference capacitance for the whole surface; a capacitivemeasurement step implemented by a capacitive measurement microprocessorelectrically connected to said capacitive support, said microprocessorbeing configured to detect a variation in capacitance of said capacitivesupport for the whole surface; and a step of transmitting a piece ofinformation representing said variation of capacitance when an absolutevalue of a difference between a capacitance measured by said capacitivemeasurement microprocessor and said reference capacitance exceeds apredetermined threshold.
 7. The method for protecting according to claim6, wherein the method further comprises a calibration step deliveringsaid reference capacitance.
 8. A payment terminal comprising: anelectronic printed circuit board comprising at least two layers; adevice for protecting the electronic printed circuit board, wherein thedevice comprises: a conductive part uniformly spread on an insulatorlayer, the entirety comprising the conductive part and the insulatorlayer forming a capacitive support presenting a uniform electrical fieldover the whole surface of one of the layers of the electronic printedcircuit board, said capacitive support being placed on the whole surfaceand being configured to deliver a reference capacitance for the wholesurface; a capacitive measurement microprocessor electrically connectedto said capacitive support, said microprocessor being configured todetect a variation in capacitance of said capacitive support for thewhole surface; and a transmitter configured for transmitting a piece ofinformation representing said variation of capacitance when an absolutevalue of a difference between a capacitance measured by said capacitivemeasurement microprocessor and said reference capacitance exceeds apredetermined threshold.
 9. A computer program comprising program codeinstructions recorded on a non-transitory computer-readable memory toimplement a method for protecting an electronic printed circuit boardcomprising at least two layers, when the program is executed by aprocessor, wherein the method comprises: laying out a conductive partuniformly spread on an insulator layer, the entirety comprising theconductive part and the insulator layer forming a capacitive supportpresenting a uniform electrical field over the whole surface of one ofthe layers of the electronic printed circuit board, said capacitivesupport being placed on the whole surface and being configured todeliver a reference capacitance for the whole surface; a capacitivemeasurement step implemented by a capacitive measurement microprocessorelectrically connected to said capacitive support, said microprocessorbeing configured to detect a variation in capacitance of said capacitivesupport for the whole surface; and transmitting a piece of informationrepresenting said variation of capacitance when an absolute value of adifference between a capacitance measured by said capacitive measurementmicroprocessor and said reference capacitance exceeds a predeterminedthreshold.